The present invention generally relates to wind turbine towers. More particularly, the present invention relates to the construction and erection of multi-column wind turbine towers.
Utility scale wind turbines built in the 1980's and 1990's comprise wind machinery set on top of simple lattice towers that are less than 60 meters tall. These simple lattice towers are similar to electrical transmission line lattice pylon structures and lattice cell towers and are designed to use minimal amounts of steel material. Additionally, the wind machinery set atop these towers is placed there with the use of large cranes.
Current land-based (onshore) utility scale wind turbine towers are limited to an average of 80 to 85 meters hub height. The most economical tower configuration is the tapered cylindrical monopole tower. The bases of the towers for the 80 meter height are 4.3 meter diameter since larger diameters cannot ship conveniently over normal highways due to interferences. The towers have reached their maximum diameter, plate thickness, and material grade. There are roughly a dozen other tower details that can overcome the transportation limitations but they are only used at about 15% of the installations. This is generally because the lift of the larger size nacelles to greater height requires larger cranes. The alternate tower details are used where the site conditions or soils will permit use of larger cranes. Larger cranes are limited in availability, rental cost, and transportation cost.
Additionally Current land-based utility scale wind turbine nacelles are limited to about 2 MW to 2.5 MW. The mass of the power nacelles is large enough at this size that very large cranes (cranes of 600 ton to 1,000 ton capacity) are required to lift the nacelles to height. There are a limited number of large cranes. It is very expensive to transport the cranes in and out of the remote project sites often requiring 100 to 150 truckloads. The allowable soil bearing capacities at many agricultural sites are not adequate for these larger cranes and extensive and expensive site improvements are required to accommodate the cranes for the large nacelle lift. A great amount of site improvement is required to move the larger cranes between individual tower pads at a given wind farm location. Extensive equipment design alterations are made to allow erection of the power nacelles in smaller components. Advancing the industry to 5 MW nacelles at 150 meter height would require a minimum of 1,250 ton capacity or larger. Industry leaders are currently installing 10 MW nacelles offshore and are in production with 12 MW nacelles for testing. These most probably would take cranes of 2,000 ton capacity or larger.
The US Department of Energy indicates that there are significantly more potential wind resources above 140 meter hub height. The 12 southeastern states have a wind potential at 80 meters of only about 8 GW but this goes to approximately 1,626 GW above 140 meters. The northeast states of OH and PA go from 1 GW to 211 GW. West coast states CA, AZ, NV and OR go from 25 GW to 538 GW. The potential for land wind in these three regions goes from only 7% to 475% of total American commercial electricity production. The wind resources near these load and population centers are more than adequate to provide for their electric power needs. Producing power from land-based wind is only about 30% of the cost of offshore and will almost certainly remain less costly than offshore regardless of the advances made in offshore installation costs. Nacelles of 8 MW are already certified and produced for offshore and designs for 10 to 15 MW nacelles will be available in less than 5 years. These larger nacelle designs could easily segue into use on land with an innovation that allows taller towers and erection of more powerful nacelles.
Multiple attempts in the prior art have been made to remedy the issue of constructing taller onshore towers that support larger nacelles. U.S. Pat. No. 8,302,365 issued Nov. 6, 2012 entitled, “Partially self-erecting wind turbine tower,” describes and illustrates a partially self-erecting wind turbine tower and a method for carrying out the assembly thereof. The invention discloses an extendable pylon column with at least three legs. The invention has legs that extend from an installed retracted position to an extreme extended position. The extendable pylons are driven by a gear to extend and then lock. The wind machinery, or nacelle is then attached to the top hub.
Additional prior art applications such as US Patent Application No. 2012/0023860A1 published Feb. 2, 2012 entitled, “Adapter Configuration for a Wind Tower Lattice Structure,” describes a lattice structured tower having a plurality of vertically oriented columns and cross-braced members. The disclosure of the wind tower construction comprising a lattice structure with vertically oriented columns and cross-braced members, as well as an adapter molded onto the top of the lattice structure such that the top portions of the columns are embedded into the adapter provides a mostly conventional structure. The invention discloses that the adapter be poured of concrete, with the columns embedded in said adapter.
Additional prior art applications such as US Published Patent Application No. 2015/0167644A1 published Jun. 18, 2015 entitled, “Lattice tower assembly for wind turbines,” describes a lattice tower assembly for a wind turbine. The invention discloses a lattice tower assembly comprising a plurality of structural members connected together to define an open lattice tower, the structural members comprising a plurality of outer cross-support members, the inner and outer cross-support members being connected between the supports so as to define one or more openings, wherein each of the inner cross-support members overlaps one of the outer cross-support members. The invention also discloses a lattice tower covering comprised of panel elements. The design of the invention seeks to remedy the size restrictions of larger turbines.
In yet another prior art reference, U.S. Pat. No. 7,993,107 granted Aug. 9, 2011 entitled, “Onshore wind turbine with tower support system,” describes a tower support system provides support to the tower and includes an axially extending circumferential sleeve mounted around the tower. Therein is disclosed a tower with a nacelle, a tower base end configured for support on a ground level foundation, and tower support system. The tower is constructed of tubular members with a constant diameter around the location of the support sleeve. The sleeve is constructed in a concentrically spaced location with the tubular supports equally spaced around the sleeve.
In yet another prior art reference, U.S. Pat. No. 7,735,290 granted Jun. 15, 2010 entitled, “Wind turbine assembly tower,” describes a method for constructing a turbine tower with a first section having three legs. The invention discloses the first tower comprising three legs diverging from the longitudinal axis forming a first tower section. Additionally, it discloses a second tower section coupled to the first, with an additional leg extending parallel to the legs of the first section. It also discloses shear panels connecting between adjacent upper sections and the legs to increase torsion stiffness. The lower legs extend out further from the midpoint of the tower, with the upper legs being near vertical in position.
What is needed is an efficient, cost effective wind turbine structure which comprises a sturdy and robust configuration that is capable of reaching greater heights and which can be transported to the erection site over the nation's highways without violating transportation restrictions. Also needed is a method of erecting said taller wind turbine tower structure and heavy topside mechanisms without the need for the physically large and heavy lift cranes that are now standard within this industry or the use of a separate temporary lift tower.